Parallel scan distributors and collectors and process of testing integrated circuits

ABSTRACT

An integrated circuit ( 70 ) having parallel scan paths ( 824 - 842, 924 - 942 ) includes a pair or pairs of scan distributor ( 800,900 ) and scan collector ( 844,944 ) circuits. The scan paths apply stimulus test data to functional circuits ( 702 ) on the integrated circuit and receive response test data from the functional circuits. A scan distributor circuit ( 800 ) receives serial test data from a peripheral bond pad ( 802 ) and distributes it to each parallel scan path. A scan collector circuit ( 844 ) collects test data from the parallel scan paths and applies it to a peripheral bond pad ( 866 ). This enables more parallel scan paths of shorter length to connect to the functional circuits. The scan distributor and collector circuits can be respectively connected in series to provide parallel connections to more parallel scan paths. Additionally multiplexer circuits ( 886,890 ) can selectively connect pairs of scan distributor and collector circuits together. The scan distributor and collector circuits can be formed in core circuits ( 704 ). The core circuits then can be connected to other core circuits and functional circuits with simple connections to the parallel scan circuits through the scan distributor and collector circuits.

This application is a divisional of prior application Ser. No.12/033,175, filed Feb. 19, 2008, currently pending;

Which was a divisional of prior application Ser. No. 11/775,472, filedJul. 20, 2007, now U.S. Pat. No. 7,355,430, granted Apr. 8, 2008;

Which is a divisional of prior application Ser. No. 11/235,572, filedSep. 26, 2006, now U.S. Pat. No. 7,256,601, granted Aug. 14, 2007;

Which was a divisional of prior application Ser. No. 10/695,241, filedOct. 28, 2003; now U.S. Pat. No. 6,985,001, granted Jan. 10, 2006;

Which was a divisional of prior application Ser. No. 09/997,540, filedNov. 29, 2001, now U.S. Pat. No. 6,646,460, granted Nov. 11, 2003;

Which was a divisional of prior application Ser. No. 09/836,675, filedApr. 16, 2001, now U.S. Pat. No. 6,362,015, granted Mar. 26, 2002;

Which was a divisional of prior application Ser. No. 09/183,885, filedOct. 30, 1998, now U.S. Pat. No. 6,242,269, granted Jun. 5, 2001;

Which claimed priority from Provisional Application Ser. No. 60/064,145,filed Nov. 3, 1997.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to testing of integrated circuits usingparallel scan paths and particularly relates to testing those integratedcircuits using serial to parallel and parallel to serial registers tomove test information to and from the integrated circuit.

2. Description of the Related Art

Cost effective testing of today's complex integrated circuits isextremely important to semiconductor manufacturers from a profit andloss standpoint. The increases in complexity of state-of-the-artintegrated circuits is being accompanied by an ever increasingdifficulty to test the integrated circuits. New test techniques must bedeveloped to offset this increasing integrated circuit test cost,otherwise further advancements in future integrated circuit technologymay be blocked. One emerging technology that is going to accelerate thecomplexity of integrated circuits even more is intellectual propertycores. These cores will provide highly complex pre-designed circuitfunctions such as; DSPs, CPUs, I/O peripherals, memories, and mixedsignal A/D and D/A functions. These cores will exist in a library andcan be selected and placed in an integrated circuit to quickly provide acomplex circuit function. The low cost testing of integrated circuitsthat contain highly complex core functions will be a significantchallenge.

SUMMARY OF THE INVENTION

The present invention provides a way to amplify test data input to andoutput from an integrated circuit by use of pad resident circuitsdescribed as parallel scan distributors, PSDs, and parallel scancollectors, PSCs. The scan distributor circuits amplify the number ofparallel serial data inputs to the integrated circuit's functionalcircuitry, and the scan collector circuits amplify the number ofparallel serial data outputs from the integrated circuit's functionalcircuitry.

Additionally, the invention provides a way to test complex cores or corecircuits embedded within integrated circuits by reuse of scandistributor circuits and scan collector circuits located at the I/Oterminals of the core. In this aspect of the present invention, coreresident scan distributor and collector circuits amplify the test datainput to and output from the core circuitry, similar to that describedfor the integrated circuit having no core circuits.

Further, the invention provides a way concurrently to test core and noncore circuitry within an integrated circuit. In this aspect of thepresent invention, the scan distributor and collector circuits residingat the bond pads of the integrated circuit are serially linked with scandistributor and collector circuits residing at core I/O terminals toprovide massive parallel test data input to and output from circuitrywithin the integrated circuit.

The invention described below facilitates parallel scan testing by useof the scan distributor and scan collector circuits. The scandistributor circuit is basically a serial-input parallel-output shiftregister, and the scan collector circuit is basically a parallel-inputserial-output shift register. While these distributor and collectorcircuits can be of any bit length, one embodiment shows the distributorand collector circuits being 10 bits deep. With 10 bit deep distributorand collector circuits, the number of scan paths each pad can access ismultiplied by a factor of 10. By amplifying the number of scan paths apad can access, the functional circuitry of the integrated circuit canbe partitioned into many more shorter scan paths, reducing the test timeof the integrated circuit by reducing the test data shift in/shift outtime. For example, using 10 bit scan distributor and collector circuits,an integrated circuit with 200 bond pads (100 bond pad pairs) availablefor transferring test data can concurrently access 1000 parallel scanpaths.

BRIEF DESCRIPTION OF THE VIEWS OF THE DRAWINGS

FIG. 1 depicts an integrated circuit.

FIG. 2 is a block diagram of a known parallel scan path testarrangement.

FIG. 3 is a block diagram of a parallel scan path test arrangementaccording to the present invention.

FIG. 4 is a block diagram of the scan path test arrangement of FIG. 3further including a test controller according to the present invention.

FIG. 5 is a flow chart illustrating operation of the test controller andscan path arrangement of FIG. 4.

FIG. 6 is a flow chart illustrating an alternate operation of the testcontroller and scan path arrangement.

FIG. 7 depicts an integrated circuit that includes an embedded core.

FIG. 8 is a block diagram of a scan test circuit and controllerarrangement for testing the integrated circuit and core of FIG. 7according to the present invention.

FIG. 9 depicts an integrated circuit including an embedded core, inwhich the embedded core itself includes an embedded core.

FIG. 10 is a block diagram of a scan test circuit and controllerarrangement for testing the integrated circuit and embedded cores ofFIG. 9 according to the present invention.

FIG. 11 is a block diagram of a hierarchical connection between scantest circuit arrangements according to the present invention.

FIG. 12 is a block diagram of an arrangement of scan test circuits andcontrollers using multiplexer circuitry according to the presentinvention.

DETAILED DESCRIPTION

In FIG. 1, integrated circuit 100 comprises a semiconductor substrate102 with bond pads 104 and functional circuitry 106. To expeditetesting, an integrated circuit's functional circuitry 106 can bearranged into many parallel scan paths, each scan path having a serialdata input and serial data output. Having many short parallel scanpaths, versus one long continuous scan path, is preferred since itreduces the time it takes to shift test data in and out. Each parallelscan path's serial data input and output can be connected to a bond pad104 to allow a tester to input test data to and output test data fromall scan paths concurrently. Parallel scan design references includeFIG. 18-3 of Chapter 18 of 1990 IEEE Publication “The Test Access Portand Boundary Scan Architecture” by Colin Maunder, and FIG. 14a of U.S.Pat. No. 5,526,365 to Whetsel.

In FIG. 2, known parallel scan path 200 has a serial data input at pad202 and a serial data output at pad 204. Known parallel scan path N 206has a serial data input at pad 208 and a serial data output at pad 210.In the circuits of FIG. 2, N scan paths will require use of 2.times.Nbond pads for serial data input and serial data output. While some bondpads will be used to supply control to the scan paths and for power andground, a majority of the bond pads may be used for scan path serialdata input and output. The number of available bond pad pairs will limitthe number of scan paths that can be accessed in parallel.

The scan cycle time of the conventional scan path arrangement of FIG. 2can be expressed by (L+1)T, where L is the scan path length throughwhich stimulus and response test patterns are shifted during each scancycle, 1 is the capture step required to input response data from thefunctional logic under test into the scan path, and T is the period ofthe scan clock. Using this equation, for example, the scan cycle timefor a scan path having a length (L) of 1000 bits is (1000+1)T, or 1001T.The test time equals “scan cycle time” times “the number of testpatterns”.

In FIG. 3, scan test circuit 301 includes a scan distributor 300, scanpaths 324 through 342 and scan collector 344. Parallel scan distributorcircuit 300 forms a data input amplification circuit connected betweenbond pad 302 and data inputs 304 through 322 to ten plural scan paths324 through 342, of which only the first and last are depicted forclarity of the drawing. Parallel scan collector circuit 344 forms anoutput amplification circuit connected between the data outputs 346through 364 of plural scan paths 324 through 342 and bond pad 366.

Scan test circuit 367 includes a scan distributor 368, scan paths 392through 410 and scan collector 412. In a like manner, parallel scandistributor circuit 363 forms a data input amplification circuitconnected between bond pad 370 and data inputs 372 through 390 to tenplural scan paths 392 through 410, of which only the first and last aredepicted for clarity of the drawing. Parallel scan collector circuit 412forms an output amplification circuit connected between the data outputs414 through 432 of plural scan paths 392 through 410 and bond pad 434.

Scan paths 324 through 342 form one group of scan paths connectedbetween scan distributor circuit 300 and scan collector circuit 344.Scan paths 392 through 410 form another group of scan paths connectedbetween scan distributor circuit 368 and scan collector circuit 412.

In FIG. 3, the parallel scan distributor provides a data inputamplification circuit located between a bond pad and data inputs toplural scan paths. The parallel scan collector provides a data outputamplification circuit located between the data outputs of the pluralscan paths and a bond pad. This is different from the conventionalparallel scan path arrangement depicted in FIG. 2 in which each scanpath's data input is directly connected to a bond pad and each scanpath's data output is directly connected to a bond pad. Therefore, thedata amplification capability of the present invention is understood bycomparing FIG. 2 and FIG. 3.

The conventional parallel scan path arrangement of FIG. 2 thus ismodified by the insertion of parallel scan distributor circuits andparallel scan collector circuits. The scan distributor circuits 300, 368are basically serial-input parallel-output shift registers, and the scancollector circuits 344, 434 are basically parallel-input serial-outputshift registers. While the parallel input and output width of the scandistributor and collector circuits can be of any bit width, thedistributor and collector circuits 300, 344, 368 and 412 have 10 bitwide parallel inputs and outputs that provide one bit input and outputto the respective parallel scan paths.

The scan input modifications of the FIG. 2 arrangement include: (1)disconnecting the bond pads from scan paths 1-N, (2) inserting the scandistributor circuits, (3) connecting the bond pads to the serial inputsof the scan distributor circuits, and (4) connecting each paralleloutput of the scan distributor circuits to a respective input of thescan paths. The scan output modifications of the FIG. 2 arrangementinclude: (1) disconnecting the bond pads from scan paths 1-N, (2)inserting the scan collector circuits, (3) connecting the bond pads tothe serial outputs of the scan collector circuits, and (4) connectingthe output of each scan path to a respective parallel input of the scancollector circuits.

The scan path modifications of the FIG. 2 arrangement include: (1)dividing each scan path 1-N into a group of individual shorter lengthscan paths, each preferably being of equal length, and in which thenumber of individual scan paths of each group equals to the number ofparallel inputs and outputs (10) of the scan distributor and scancollector circuits, (2) connecting the serial data input of each scanpath of each group to a parallel output of a respective scan distributorcircuit, and (3) connecting the serial data output of each scan path ofeach group to a parallel input of a respective scan collector circuit.

With 10 bit deep scan distributor and collector circuits, the number ofindividual scan paths in each group is equal to ten. If the scan paths200 and 206 of FIG. 1 were each 1000 bits long, the above partitioningwould convert each 1000 bit scan path into a group often 100 bit scanpaths.

In FIG. 4, integrated circuit 446 includes scan test circuits 448. Onescan distributor 450 and scan collector 452 pair provide access to 10parallel scan paths 454 through 472. Each of the 10 parallel scan pathsconnects to combinational logic 474 in functional circuitry 106. Thecombinational logic 474 is tested by inputting test stimulus andoutputting test response through the parallel scan paths 454 through472. While stimulus input and response output connections are shown onlybetween combinational logic 474 and parallel scan path 1 454, all ten ofthe parallel scan paths 454 through 472, respectively, are similarlyconnected to combinational logic 474.

A controller 476 connects to the scan distributor circuit 450, parallelscan paths 1-10 454 through 472 and scan collector 452, as well as allother scan distributors, parallel scan paths, and scan collectors in theintegrated circuit by leads 482. Controller 476 controls the testoperation of the scan distributor circuits, parallel scan paths 1-10 454through 472 and scan collector 452, as well as all other scandistributors, parallel scan paths, and scan collectors in the integratedcircuit. The controller 476 connects to bond pads 478 and 480 for accessand control by a source external to the integrated circuit, such as awafer or integrated circuit tester.

In FIG. 4, integrated circuit 446 includes scan test circuits 448. Onescan distributor 450 and scan collector 452 pair provide access to 10parallel scan paths 454 through 472. Each of the 10 parallel scan pathsconnects to combinational logic 474 in functional circuitry 106. Thecombinational logic 474 is tested by inputting test stimulus andoutputting test response through the parallel scan paths 454 through472. Parallel stimulus input connections 482 and parallel responseoutput connections 484 are between combinational logic 474 and all tenof the parallel scan paths 454 through 472, respectively.

The combinational logic 474 is tested by receiving test stimulus datafrom the parallel scan paths 454 through 472 and outputting testresponse data to the parallel scan paths 454 through 472. The teststimulus data applied to the combinational logic 474 from the parallelscan paths is input to the parallel scan paths via the scan distributor450. The test response data received into the parallel scan paths fromthe combinational logic is output from the parallel scan paths via thescan collector 452. During test, the controller 476 operates the scandistributor 450, parallel scan paths 454-472, and scan collector 452 totest the combinational logic 474. Simultaneous with this test, thecontroller 476 also operates other scan distributors, parallel scanpaths, and scan collectors of the integrated circuit to test furthercombinational logic within the integrated circuit.

In FIG. 5, the flow chart illustrates one example of the controlleroperating the scan distributor, parallel scan paths, and scan collectorof FIG. 4 during testing of the integrated circuit's combinationallogic. Initially, the controller will be in the start test state waitingfor a signal to start testing. In response to a start test signal, thecontroller executes the following steps. The step numbers correspond tothe state numbers in the diagram of FIG. 5.

1 Step Number Operation 501 Test to see if start test has occurred. No,goto 501. Yes, goto 502. 502 configure functional circuitry into testmode, goto 503 503 Capture response data outputs from all parallel scanpaths (PSPs) into scan collector (PSC), goto 504 504 Shift scandistributor and collector ten times to load stimulus data intodistributor and unload response data from collector, goto 505 505 Shiftscan paths one time to load scan paths with test stimulus data from scandistributor, goto 506 506 Test to see if parallel scan paths (PSPs) havefilled with the test stimulus pattern No, goto 503 Yes, goto 507 507Test to see if end of test has occurred No, goto 508 Yes, goto 509 508Capture response pattern from combinational logic into parallel scanpaths (PSPs), goto 503 509 End of test, configure IC circuitry intonormal mode, goto 501

Following the end of test step 507, the test is complete and thecontroller configures the functional circuitry back into its normalmode, then goes to and remains in the start test state 501 until anotherstart test signal occurs. During the test, a tester supplies stimulusdata to the scan paths via the serial to parallel operation of the scandistributors, and receives response data from the scan paths via theparallel to serial operation of the scan collectors. The tester comparesthe response data it receives from the scan collectors to expectedresponse data to determine if the test passes or fails. Alternately,during test the tester may compress the response data it receives fromthe scan collectors into signatures and then compare the signatures atthe end of test to expected signatures.

In FIG. 6, an example of another controller flow chart illustrates howthe decision states 506 and 507 of FIG. 5 may be merged into state 605of FIG. 6 to streamline the test execution flow. In FIG. 6, state 605executes the shift operation that moves data from the scan distributorsinto the scan paths, then executes decision states to determine whetherthe next state will be state 503, 508, or 509. Merging the decisionstates into state 605 is possible because the decisions regarding thefull/not full status of the scan paths and the end of test are easilypredictable conditions.

2 Step Number Operation 501 Test to see if start test has occurred No,goto 501 Yes, goto 502 502 Configure IC circuitry into test mode, goto503 503 Capture response data outputs from all parallel scan paths intoscan collectors, goto 504 504 Shift scan distributors & scan collectorsten times to load stimulus data into scan distributors and unloadresponse data from scan collectors, goto 605 605 Shift scan paths onetime to load scan paths with test stimulus data from scan distributors,then If scan path is not filled, goto 503 If scan path is filled & notend of test, goto 508 If scan path is filled & end of test goto 509 508Capture response pattern from combinational logic into scan paths, goto503 509 Configure IC circuitry into normal mode, goto 501

While the test data input and output bandwidth of the scan paths 454through 472 is reduced by the serial to parallel translation in scandistributor 450 and parallel to serial translation in scan collector 452that occurs for each datum shifted into and out of the parallel scanpaths. The overall test time however is comparable to the conventionalparallel scan test times for the circuits of FIG. 2. The reason for thisis that scan distributor and scan collector circuits enable test data tobe communicated to a larger number of shorter length parallel scanpaths, whereas the conventional parallel scan arrangement of FIG. 2communicates test data to a lesser number of longer length scan paths.

The scan cycle time of the scan distributor and scan collectorarrangement of FIG. 4, using the FIG. 6 controller operation steps, canbe expressed by equation ((D+2)L+1)T, where: (D+2) is the scan depth (D)of the scan distributor and scan collector circuits shifted, step 504;plus 2, the shifting of data between scan distributor and scan paths instep 605, and between scan collector and scan paths in step 503; L isthe scan path length through which data is shifted during each scancycle; plus 1, the capture step 508 required to input data from thecombinational logic into the scan paths; and T is the period of the scanclock.

For the purpose of illustrating a comparison of the scan cycle timesbetween the conventional path arrangement of FIG. 2 and the scandistributor and scan collector scan path arrangement of FIG. 4, the L inthe scan distributor and scan collector scan cycle time equation abovecan be expressed in terms of the L in the conventional scan cycle timeequation. As previously described in regard to FIG. 3, a conventionalscan path having a length (L) can be converted into a group of tenindividual scan paths each having a length of L/10, when using 10 bitscan distributor and scan collector circuits. Converting the originalconventional scan path of FIG. 2 into an equivalent scan distributor andscan collector scan path arrangement does not modify the stimulus andresponse connections to the combinational logic, it simply partitionsthe single conventional scan path into an equivalent group of shorterlength scan paths. Therefore, for the purpose of comparing scan cycletimes between the conventional scan path arrangement of FIG. 2 and aconverted, but equivalent, stimulus and response connection, scandistributor and scan collector scan path arrangement of FIG. 4, L/10 issubstituted for L in the scan distributor and scan collector scan cycletime equation above.

This results in a scan distributor and scan collector scan cycle timeequation of: ((D+2)(L/10)+1)T, or ((10+2) (L/10)+1)T, or (1.2L+1)T,where: L equals the bit length of the original scan path of FIG. 2, andD equals the depth (i.e. 10 bits) of the scan distributor and scancollector circuits. Substituting L=1000 into the conventional scan pathequation, (L+1)T, of FIG. 2 and scan distributor and scan collectorequation, (1.2L+1)T, above, results in 1001T and 1201T, respectively. Incomparing 1001T to 1201T, it is seen that the conversion of theconventional scan path arrangement into an equivalent scan distributorand scan collector scan path arrangement only extends the scan cycletime by approximately 16.6%, in this example.

The scan distributor and scan collector scan cycle time advantageouslyapproaches the conventional scan test time as the depth of the scandistributor and scan collector circuits increase, since test data may becommunicated to a larger number of shorter length parallel scan paths.For example, with 40 bit deep scan distributor and scan collectorcircuits connected to forty 25 bit scan paths, converted from the FIG. 2scan path as described above, the scan distributor and scan collectorscan cycle time becomes (40+2) (L/40)+1)T, or (1.05L+1)T, which extendsthe scan cycle time by approximately 4.7% compared to the conventionalscan cycle time. For identical combinational logic being tested, thenumber of scan cycles required to apply the test patterns is the samefor both the scan distributor and scan collector and conventional scanpath arrangements. The integrated circuit test time will therefore beextended in proportion to the scan cycle time extension.

In FIG. 7, an IC 700 contains within its functional circuitry 702 acomplex core circuit 704, such a DSP. The IC's functional circuit 702contains other circuits besides the core. IC 700 includes peripheralbond pads 706 and core circuit 704 includes its own set of peripheralterminals 708. In this example, both the IC 700 and core 704 have beendesigned to include the previously described invention comprising scandistributor and scan collector circuits, parallel scan paths, and thecontroller 476.

In FIG. 8, the IC 700 includes functional circuit and core circuit scandistributor and scan collector architectures. The view is simplified inthat it depicts only one exemplary pair of scan distributor and scancollector circuits for each of the functional and core circuits.

In FIG. 8, functional scan test circuits 801 associate with functionalcircuits 702. Parallel scan distributor circuit 800 forms a data inputamplification circuit connected between bond pad 802 and data inputs 804through 822 to ten plural scan paths 824 through 842, of which only thefirst and last are depicted for clarity of the drawing. Parallel scancollector circuit 844 forms an output amplification circuit connectedbetween the data outputs 846 through 864 of plural scan paths 824through 842 and bond pad 866. Bond pads 802 and 866 are part ofperipheral bond pads 706 of the functional circuits 702.

A controller 876 connects to the scan distributor circuit 800, parallelscan paths 1-10 824 through 842 and scan collector 844, by leads 882.Controller 876 controls the test operation of the scan distributorcircuit 800, parallel scan paths 1-10 824 through 842 and scan collector844. The controller 876 connects to bond pads 878 and 880 for access andcontrol by a source external to the integrated circuit 700, such as awafer or integrated circuit tester. Bond pads 878 and 880 are part ofperipheral bond pads 706.

In core circuits 704, core scan test circuits 901 associate with corecircuits 704. Parallel scan distributor circuit 900 forms a data inputamplification circuit connected between terminal 902 and data inputs 904through 922 to ten plural scan paths 924 through 942, of which only thefirst and last are depicted for clarity of the drawing. Parallel scancollector circuit 944 forms an output amplification circuit connectedbetween the data outputs 946 through 964 of plural scan paths 924through 942 and terminal 966. Terminals 902 and 966 are part of corecircuit terminals 708 of the core circuits 704.

A controller 976 connects to the scan distributor circuit 900, parallelscan paths 1-10 924 through 942 and scan collector 944, by leads 982.Controller 976 controls the test operation of the scan distributorcircuit 900, parallel scan paths 1-10 924 through 942 and scan collector944. The controller 976 connects to terminals 978 and 980 for access andcontrol by controller 876 over leads 984 and 986. Terminals 978 and 980are part of core circuit terminals 708.

Scan distributor 800 has a serial output on lead 884 connecting to oneinput of multiplexer 886. The other input of multiplexer 886 receives asignal FI. The sole output of multiplexer 886 connects on lead 888 toterminal 902. Terminal 966 connects to the sole input of demultiplexer890. One output of demultiplexer 890 on lead 892 connects to a serialinput of scan collector 844. The other output of demultiplexer 890connects to a signal FO. Controller 876 connects to the multiplexer 886on lead 894 and connects to the demultiplexer 890 on lead 896.

In the IC 700, the scan distributor 800 and scan collector 844 circuitsare associated with the I/O bond pads for the integrated circuit 700. Inthe core 704, the scan distributor 900 and scan collector 944 circuitsare associated with the I/O terminals for the core circuits 704. Thescan distributor 800 and scan collector 844 circuits are the same asdescribed in regard to FIG. 4, except that the scan distributor circuit800 has been provided with a serial output 884 and the scan collector844 circuit has been provide with a serial input 892. The core's scandistributor 900 and scan collector 944 circuits are the same as scandistributor 800 and scan collector 844 circuits with two exceptions:they are associated with the core's terminals 902 and 966 and they haveno serial output 884 or serial input 892.

A multiplexer 886, or other type of connection circuit, is provided ateach core terminal that has a scan distributor, and a demultiplexer 890,or other type of connection circuit, is provided at each core terminalthat has a scan collector. The multiplexer allows inputting either afunctional input signal or test input to the core terminal. Thedemultiplexer allows outputting either a functional output signal ortest output from the core terminal.

The test input to the multiplexer 886 comes from the serial output ofthe IC's scan distributor circuit 800, and the test output from thedemultiplexer 890 goes to the serial input of the IC's scan collectorcircuit 844. The functional input and output, FI and FO, are connectedto neighboring circuits within the IC. During normal mode, the IC'scontroller 876 controls the multiplexers and demultiplexers at the coreterminals to input and output the functional signals. In test mode, thecontroller 876 controls the multiplexers and demultiplexers to input andoutput test signals.

Controller 976 is not directly connected to the peripheral bond pads 878and 880 as is controller 876. Rather, controller 976 for the corecircuits is connected indirectly to the peripheral bond pads via thecontroller 876. Controller 876 has authority over the core's controller976 in that controller 876 can enable, disable or modify the operationmodes of controller 976. However, during test the controllers mayoperate together to synchronize the operation of the scan distributorand scan collector circuits of the IC and core.

As will be seen in embodiments to be described, this controllerinterconnect technique is maintained between controllers that arearranged hierarchically within an integrated circuit. Also, theauthority of a higher level controller over a lower level controller ismaintained in controllers arranged within a hierarchy. Furthermaintained is the ability of hierarchical controllers to synchronizethemselves during test so that the operation of all hierarchicallylinked scan distributor and scan collector circuits, associated with thecontrollers, occur synchronously.

Testing, using the IC and core scan distributor and scan collectorcircuits of FIG. 8, is the same as previously described for the circuitsof FIG. 4 with two exceptions. The serial data input to the core's scandistributor circuit 900 passes through the IC's scar. distributorcircuit 800 and the serial data output from the core's scan collectorcircuit 944 passes through the IC's scan collector circuit 844. Threetypes of testing car occur on the IC 700: (1) testing of the IC'sfunctional non-core circuitry, (2) testing of the core circuitry, and(3) simultaneous testing of both the IC's non-core circuitry and thecore circuitry.

When the IC's non-core circuitry is being tested, but the core is notbeing tested, the core's controller 976 is disabled by the IC'scontroller 876 and the multiplexer 886 and demultiplexer 890 disconnectthe core's terminals from inputting or outputting functional signals toneighboring IC circuitry. In this mode the core is quiet and its I/O isdisabled from disturbing testing being performed on the non-corecircuitry.

When the core is being tested, but the non-core circuitry is not beingtested, the core's controller 976 is enabled by the IC's controller 876.The IC's controller 876 controls the core terminal multiplexer 886 anddemultiplexer 890 such that the serial data output from the IC's scandistributor circuit 800 is input to the core's scan distributor circuit900, and the serial data output from the core's scan collector circuit944 is input to the IC's scan collector circuit 944. Further, the ICcontroller 876 disables the non-core scan paths from shifting andcapturing data and causes the scan distributor 800 and scan collectorcircuits 844 to operate as test data pipeline registers between the ICpads 802 and 866 and the core's scan distributor 900 and scan collector944. During test, the core's scan distributor 900 and scan collector 944circuits are controlled by the core's controller 976 to operate asdescribed in regard to FIG. 5 or 6. The only difference is that thedepth of the scan data input to and output from the core's scandistributor 900 and scan collector 944 circuits is greater since thedata is pipelined though the IC's scan distributor 800 and scancollector 844 circuits.

When both the IC's non-core and core circuitry are being tested, boththe IC and core controllers 876 and 976 are enabled. Also the coreterminal multiplexer 886 and demultiplexer 890 are set to input testdata to the core's scan distributor 900 from the IC's scan distributor800, and to output test data from the core's scan collector 944 to theIC's scan collector 844. During test, both controllers 876 and 976 aresynchronized to the external control input from the tester via theperipheral bond pads to allow stimulus data to be scanned into both theIC and core scan distributor circuits while response data is scanned outfrom both the IC and core scan collector circuits.

The test operation of the IC and core scan distributor and scancollector circuits is identical to that previously described in regardto FIG. 5 or 6. Again, the only difference is that the depth of the scandata input and scan data output is greater since the IC and core scandistributor and scan collector circuits are serially connected. Theadvantage of testing both the IC's non-core and core circuitry at thesame time is that it reduces the test time of the IC.

These three modes of testing can be setup by scanning the IC and corecontrollers. Referring to FIG. 8, the IC controller is connected to ICpads for input and output and the core controller is connected to the ICcontroller for input and output. A tester that is connected to the ICcontroller input/output bond pads 706 can scan the controllers to set upthe type of test to be performed. After setting up the test type, thetester can input control on input pads to cause the controllers tooperate according to the way the controllers have been set up. While theIC 700 has one core, other integrated circuits may contain multiplecores. Multiple cores can be tested either individually or incombination with other cores and non-core circuits.

In FIG. 9, integrated circuit 1000 contains functional circuitry 1002,which contains first core circuitry 1004. First core circuitry 1004contains second core circuitry 1006. This hierarchical embedding of corecircuitry or cores within cores creates a very difficult testingsituation. The present invention however renders such nesting of corestestable regardless of how deeply embedded they might be within anintegrated circuit.

3 Functional circuitry 1002 is associated with bond pads 1008. Firstcore circuitry is associated with terminals 1010. Second core circuitryis associated with terminals 1012.

In FIG. 10, the scan distributor and scan collector architecture isshown hierarchically extending from the IC level to the first corelevel, and from the first core level into the second core level.Integrated circuit 1000 comprises functional scan test circuits 1014associated with functional circuitry 1002, first scan test circuits 1016associated with first core circuits 1004 and second scan test circuits1018 associated with second core circuits 1006.

In accordance with the circuits depicted in FIGS. 7 and 8, test accessto the second scan test circuits 1018 is achieved through the serialpipelines provided by the first scan test circuits 1016 and functionalscan test circuits 1014. Thus the scan distributor 1020 and scancollector 1022 circuits of second core circuits 1006 is achieved via theserial pipelines provided by the scan distributor and scan collectorcircuits 1024 and 1026 of first scan test circuits 1016 and the scandistributor and scan collector circuits 1028 and 1030 of the functionalscan test circuits 1014.

Also as described in regard to FIG. 8, all the functional circuits 1002,first core circuits 1004 and second core circuits 1006 can be testedtogether, in selected combinations, or individually. When testing all ofthe IC's circuitry together, the scan distributor and scan collectorcircuits and controllers are set up to allow the tester to input deepstimulus patterns to serially connected scan distributors and to outputdeep response patterns from serially connected scan collectors. The testis the same as described in connection with FIG. 8, only the depth ofthe serial stimulus and response patterns changes as more scandistributor and scan collector circuits are added to the IC's bond padinput and output scan operations.

In FIG. 11, integrated circuit 1100 includes peripheral bond pads 1102,functional circuits 1104 and scan test circuits 1106, 1108, 1110 and1112. Scan test circuits 1106, 1108, 1110 and 1112 are connected inseries to each of bond pads 1114 and 1116.

The scan test circuits 1106, 1108, 1110 and 1112 illustrate a simplifiedview of how scan distributor and scan collector circuits can be usedhierarchically within an IC to bring about massive parallel scantesting. Each available pair of IC bond pads can be viewed as entry andexit points to a hierarchical arrangement of embedded scan distributorand scan collector circuits. Each scan distributor and scan collectorcircuit can be serially linked to the bond pads, either directly, aswith the scan distributor and scan collector circuits 1118 and 1120, orvia intermediate scan distributor and scan collector circuits, such asscan distributor and scan collector circuits 1122 and 1124, or 1126 and1128.

In FIG. 11, 4 levels of 10 bit scan distributor and scan collectorcircuits are linked to the bond pad pair 1114, 1116 to provide a 40 bitwide test data input and output interface using only two of the IC bondpads. Each level could represent the hierarchical position of anembedded core within the IC. While not shown, all available pad pairs(i.e. pads not used for test control or power/ground) can be similarlyconnected in a hierarchical arrangement to 40 bit wide scan distributorand scan collector circuits inside the IC. A tester connected to the padpairs can transfer test data to the target test circuits residing in theIC at each hierarchical circuit level 1-4. The serial to parallel andparallel to serial test data operation of hierarchically arranged scandistributors and scan collectors is clear from FIG. 11.

In FIG. 12, integrated circuit 1200 includes scan test circuits 1202connected to bond pads 1204 and 1206. Controller 1208 connects to bondpads 1210 and 1212 and scan test circuits 1202. Integrated circuit 1200also includes core circuits 1214 that include scan test circuits 1216and core circuits 1218 that include scan test circuits 1220. Controller1222 is associated with scan test circuits 1216 and controller 1224 isassociated with scan test circuits 1220.

Multiplexer circuitry 1226 connects scan test circuits 1202 to scan testcircuits 1216 and 1220. A serial output 1228 of scan distributor 1230connects to the multiplexer 1226 and a serial input 1232 of scancollector 1234 connects to multiplexer 1226. Scan test circuits 1216connect to multiplexer 1226 through multiplexer 1236, which alsoreceives a functional input FI, and through demultiplexer 1238, whichalso provides a functional output FO. Scan test circuits 1220 connect tomultiplexer 1226 through multiplexer 1240, which also receives afunctional input FI, and through demultiplexer 1242, which also providesa functional output FO. Controllers 1222 and 1224 also connect tomultiplexer 1226 through respective leads 1244, 1246, 1248 and 1250.

Integrated circuit 1200 provides an alternate configuration for usingscan distributor and scan collector circuits whereby cores 1214 and 1218are individually selected and connected to the IC's scan distributor andscan collector circuitry and controller for testing. This selection isachieved by placing multiplexer circuitry 1226 between the IC's scandistributor 1230, scan collector 1234, and controller 1208 circuitry,and the cores. Thus the cores 1214 and 1218 can be individuallyconnected to the serial data input and output of the IC's scandistributor and scan collector circuitry and to the IC's controller. TheIC's controller supplies the control input to the multiplexer circuitryfor selecting a core for testing. Once a core is selected and connectedto the IC's scan distributor and scan collector circuitry, the core istested as previously described.

It is important to note that when the integrated circuits 446, 700,1000, 1100 or 1200 evolve into a core for use inside another integratedcircuit, their hierarchical scan distributor and scan collector testarchitectures are reusable inside that IC. The ability to reuse the testarchitecture, as well as the test patterns developed for thearchitecture, is an important feature of the present invention. Thisfeature prevents having to spend design resources and time redesigningthe core's test architecture each time the core is used inside a new IC.A core's scan distributor and scan collector test architecture can beviewed as plug and play as far as its reuse within an IC.

1. An integrated circuit comprising: A. a semiconductor substrate; B.functional circuits formed on the substrate; C. plural scan pathcircuits formed on the substrate, each of the scan path circuits havinga serial input for loading test stimulus data, a serial output forunloading test response data, parallel outputs coupled to the functionalcircuits to apply the test stimulus data to the functional circuits, andparallel inputs receiving the test response data from the functionalcircuits; D. scan distributor circuitry having a serial data input andplural parallel outputs, the parallel outputs being connected to theserial inputs of the scan path circuits, the scan distributor circuitryloading test stimulus data to the serial inputs of the scan pathcircuits, the scan distributor circuitry being free of any internalfeedback shift register circuits; E. scan collector circuitry having aserial data output and plural parallel inputs, each parallel input beingconnected to the serial output of one of the scan path circuits, thescan distributor circuitry receiving test response data from the serialoutputs of the scan path circuits.
 2. The integrated circuit of claim 1in which the scan distributor circuitry includes shift registercircuitry having plural storage locations connected in series, thestorage locations each having a serial input, a serial output and aparallel output, the parallel output being coupled to the serial inputof one of the scan path circuits.
 3. The integrated circuit of claim 1in which the scan collector circuitry includes a parallel-input,serial-output shift register, the shift register having a main serialoutput and plural storage locations connected in series, the storagelocations having a parallel input, a serial input, and a serial output,the parallel inputs of the storage locations being coupled to the serialoutputs of the scan path circuits.
 4. The integrated circuit of claim 1in which the functional circuits include combinational logic.
 5. Theintegrated circuit of claim 1 in which the scan path circuits are ofequal length.